The invention is directed to a feed unit for delivering fuel from a supply tank, especially for internal combustion engines, of the generic type defined in the preamble of claim 1
In a known feed unit of this type (DE 44 44 854 A1) designated as a so-called tank installation unit, the electric drive motor of the feed pump with its cylindrical outer jacket is received in an exact fit in the central chamber of the filter cup and is supported by its front end at a stop collar on the pump housing separate from the drive motor on the one hand and at elastic supporting elements on the underside of the filter cover on the other hand. The pump outlet opens into the central chamber from which the fuel that is sucked in flows into the annular chamber via the inlet duct provided with a check valve, then flows through the main filter and reaches the delivery line via the outlet duct. An outlet connection piece forming the end of the outlet duct at the filter cover is connected via a flexible corrugated pipe with a connection piece for the delivery line, this connection piece being arranged in a tank flange. The tank flange closes the opening provided in the supply tank for the installation of the feed unit. The filter cup is secured in the supply tank so as to be fixed against axial and radial displacement, for which purpose elastic coupling elements and means for securing against axial displacement are provided between the filter cup and the inner wall of the supply tank. Due to the fact that the filter cup is elastically or flexibly coupled to the supply tank, it is also absolutely necessary that the connection line between the outlet connection piece at the filter cover and the connection piece at the tank flange is constructed in a flexible manner. In another known feed unit (DE 37 30 930 A1), the feed pump which projects into a suction space by a suction connection piece is inserted laterally into a housing which is C-shaped in longitudinal section and the feed pump is supported axially and radially between the two legs or sides of the housing. A storage space for fuel flowing back from the internal combustion engine is provided in the housing; a return line which returns fuel opens into this storage space. The suction space communicates with the interior of the supply tank via a first suction space opening and communicates with the storage space via a second suction space opening. Both suction space openings are incorporated in wall portions of the suction space which are located opposite one another and the suction space openings are alternately opened and closed by a valve member arranged in the suction space. The valve member is actuated by a float and, when the suction space is filled, closes the second suction space opening and opens the first suction space. When the fuel level in the suction space falls below a given fuel level which, however, is still above the outlet end of the suction connection piece of the feed pump, the valve member opens the second suction space opening and closes the first suction space opening due to the fact that the float sinks along with the fuel level. Fuel can therefore flow out of the storage space into the suction space, so that a continued unimpeded flow of fuel through the feed pump is ensured.
The feed unit according to the invention with the characterizing features of claim 1 has the advantage that the housing of the electric-motor feed pump is decoupled from the filter cup. The feed pump is supported in an elastic manner axially and radially at both end sides of its housing, which also receives the electric motor, and therefore can not transmit its oscillating movement to the filter cup during operation, so that the filter cup can be rigidly fastened in the supply tank. The flexible corrugated pipe between the filter cover and the tank flange can accordingly be done away with, so that the tightness and strength problems associated with it are eliminated. The mounting of the feed pump is substantially simplified because only the suction connection piece of the feed pump projects through the opening in the base of the filter cup and the filter cup must be closed with the filter cover after the elastic sleeve has been fitted on the suction connection piece and pressure connection piece beforehand. When the filter cover is put on, the push-on cap formed at the filter cover automatically engages over the pressure connection piece and the elastic sleeve fitted thereto, so that the feed pump is automatically secured in the interior of the central chamber at a distance from the inner annular wall of the annular chamber. The two elastic sleeves serve to seal, support and, with respect to noise, decouple the feed pump in the filter cup. Advantageous further developments and improvements of the feed unit indicated in claim 1 are made possible through the features indicated in the additional claims. According to a preferred embodiment form of the invention, the filter cover has an annular closing collar which projects axially at the underside of the filter cover and which has a radial width corresponding to the clearance width of the annular chamber. The annular closing collar is inserted by its front side into the annular chamber with the intermediary of a ring seal toward the inner and outer annular chamber walls and is fixedly connected with the filter cup, preferably by means of beading or flanging of the inner and outer annular wall. The ducts formed in the filter cover for the inlet and outlet of fuel open into the closing surface of the closing collar covering the annular chamber. Supporting elements are preferably formed on at the underside of the closing collar so as to project radially and are supported at the main filter and accordingly secure the latter in the annular chamber so as to be fixed with respect to axial displacement. According to an advantageous embodiment form of the invention, the filter cover is constructed so as to be open in the area of the central chamber or has at least one access opening to the latter and a cylindrical wall area which is formed at the front side of the filter cover facing away from the filter cup and which defines a circular connection opening for a tank flange which closes an insertion opening for the feed unit in the supply tank. As a result of this structural feature, the feed unit inserted in the supply tank is automatically tightened axially and radially when the insertion opening is closed by the tank flange in the supply tank. Due to the fact that the pump outlet of the feed pump is connected directly to the annular chamber in the filter cup by means of its pressure connection piece at the inlet duct formed in the filter cover and the fact that the fuel return line is guided directly into the filter cup, the feed unit according to the invention with the characterizing features of claim 11 has the advantage that the central chamber in the filter cup is always filled with fuel, so that when the fuel level in the suction space arranged below the filter cup falls due to the opening of the blocking member, the suction space is refilled with fuel from the central chamber and the feed pump continues to deliver fuel in an unimpeded manner via its suction connection piece. A temporary drop in the fuel level in the suction space of the kind mentioned above occurs at low filling levels in the supply tank when the vehicle tilts toward the side as a result of driving through curves. The suction space then empties through the first suction space opening when the second suction space opening is closed by the blocking member, and the suction connection piece would emerge from the fuel volume if fuel did not flow back out of the central chamber according to the invention due to the sinking of the blocking member. The feed unit accordingly achieves a distinctly improved curving behavior at a minimum fill level in the supply tank. A compact tank constructional unit which can be produced economically and mounted without difficulty in a simple, economical manner is provided through the use of the central chamber of the filter cup as a storage space for the returning fuel.
In order to prevent the unblocking of the second suction space opening, for example, when the vehicle is parked on a hill, in spite of a possible flow of fuel out of the suction space into the supply tank, which results in the elimination of the buoyancy of the blocking member and therefore in the loss of its blocking function, it is suggested in a second embodiment example that the blocking member is provided with a hydraulically controllable contact pressing device. This contact pressing device is only effective in the inoperative state of the feed pump and its operation is canceled during feed operation due to a hydraulic pressure generated by the feed pump. As a result of this step, a sufficient supply of fuel to the feed pump is ensured even under extreme conditions.
Through the combination of the feed unit according to the invention with the characterizing features of claim 1 and the feed unit according to the invention with the characterizing features of claim 11 in accordance with a preferred embodiment form according to claim 10, the separate advantages are not only unified, but duplicate structural component parts are also economized on, so that a reduction in cost is achieved. A supply tank with an insertion opening for the feed unit according to the invention and a tank flange closing the insertion opening is indicated in claims 17 and 18.